Download 1. Why is the Krebs cycle so important in metabolism? The Krebs

1. Why is the Krebs cycle so important in metabolism?
The Krebs cycle is the point of entry and exit of many critical molecules in
respiration and metabolism. This includes all major calorie sources:
carbohydrates, lipids, and proteins.
2. Why is oxygen necessary for the respiration of fat?
Fatty acids from fat breakdown enter the Krebs cycle as acetyl CoA. The Krebs
cycle requires NAD+ and FAD to operate and these are only available as fast as
oxygen can remove electrons from the final cytochrome of the ETS.
3. Of what adaptive value is the alternative pathway of respiration in plants?
The alternative respiration pathway in plants is adaptive since it produces heat.
The higher temperature helps specific organic compounds evaporate, producing
odors that attract insects for pollination. This can also be used to melt snow by
plants that emerge in early spring.
4. How do plants and animals benefit from the heat energy released in respiration?
Many animals use respiratory heat to help maintain body temperature and
insure predictable enzyme catalyzed reaction rates. Some plants use the heat to
enhance the chances of pollination.
5. Discuss the control of glucose oxidation and ATP production in cells.
The regulation of glucose oxidation is characterized by negative feedback. When
oxygen is available, one of the glycolytic enzymes (phosphofructokinase) is
inhibited by the high levels of ATP being produced. When oxygen is lacking,
ATP production slows down and ADP builds up. The ADP stimulates
phosphofructokinase activity and increases the rate of glycolysis.
6. Describe how fats and proteins are brought into the Krebs cycle.
Fatty acids break down to acetyl CoA, which enters the Krebs cycle. Proteins are
degraded to amino acids, which are deaminated (NH2 is removed), forming
urea. The resulting carbon skeletons become 4 or 5-carbon acids, which enter the
Krebs cycle.